Genes have different forms. The term allele refers to the variant form of a gene. For example, a gene for eye color has variations of alleles that include an allele for brown eyes, blue eyes, black eyes, etc.

C. alleles

A. The recessive trait seems to disappear

Ex: If AA and aa were to breed, all there offspring would be Aa, Aa, making them tall, but they still carry the short genes.

A. The recessive trait *seems* to disappear

A Punnett square diagram represents the alleles present in an organism and gives us the genetic variations formed during a cross. To show the probability of an offspring having a particular genotype, this diagram is used.

A. probable outcome of a cross

A homozygous organism contains identical alleles, whether dominant or recessive, on both homologous chromosomes. If an organism is homozygous, it has identical alleles for a single trait.

C. homozygous

A phenotype refers to the observable characteristics of an organism such as its physical appearance and behavior.

C. phenotype

When there are more than two possible alleles that can exist in a particular population, it is said to be that an individual gene has more than two forms. This condition is known as multiple alleles.

D. multiple alleles

The illustration best describes the metaphase I stage of meiosis. In metaphase I, the fibers begin to attach into the chromosomes.

D. metaphase I

During meiosis, the diploid cell goes through a process of reduction division wherein 4 haploid cells are formed. Each haploid cell contains half the number of chromosomes in a diploid cell.

D. four haploid gamete cells

The process of meiosis ensures that the chromosome number is maintained in an organism by splitting the chromosome number of a diploid cell in gamete production. As a result, the number of chromosomes is reduced in half in a haploid cell. Once fertilization takes place, the two sex cells will combine and it will restore the number of chromosomes in a diploid cell.

D. be produced by meiosis

A gene map is used to show the relative location and the distances between genes. By determining the recombination frequency of genes during crossovers, the relative distance between genes can be mapped.

B. the relative locations of genes on a chromosome

The four principles of genetics are the listed below.

a. Principle of Dominance
This states that some alleles are dominant, and some alleles are recessive. Dominant alleles exhibit their effect in the form of a trait in an organism. On the other hand, recessive allele is masked by the dominant allele. It would only show if it is teamed up with another recessive allele.

b. Principle of Segregation
This explains how genes are separated during meiosis. During the formation of gametes in an organism, the pair of alleles segregate from each other in order for each gamete to carry one of the two alleles. In this way, an offspring acquires one allele from each parent.

c. Biological Inheritance
Biological inheritance is influenced by chemical factors that determine the traits which are passed to the next generation. This chemical factor is called genes. Genes produce the characteristics of an organism’s trait in two contrasting forms called alleles.

d. Principle of Independent Assortment
Independent assortment happens when a pair of genes separates independently during metaphase I in meiosis. In this stage, there are random combinations of genes that are formed. Genetic variation was made possible because of this principle.

Probability is the term used to describe the likelihood that some event will occur. In relation to genetics, the principle of probability allows us to predict the possible combinations of phenotypes in a genetic cross by using a diagram called Punnett squares. This diagram represents alleles and gives us the genetic variations formed during a cross.

Let us use capital letter Y to represent the dominant allele for yellow seeds and letter y to represent the recessive allele for green seeds.

Y = yellow seeds (dominant)
y = green seeds (recessive)

If two heterozygous parents with a genotype of Yy are crossed, the possible combination of genotypes in their offspring would be YY, Yy, Yy, and yy. This can be shown in the Punnett square diagram below.

Results:
3 possible genotypes
a. YY = 25%
b. Yy = 50%
c. yy = 25%

Therefore, the genotypic ratio of the offspring produced is 1:2:1.

If two heterozygous parents with a genotype of Yy are crossed, the possible combination of genotypes in their offspring would be YY, Yy, Yy, and yy. Therefore, the genotypic ratio of the offspring produced is 1:2:1.

Genes have different forms. The term allele refers to the variant form of a gene. For example, a gene for eye color has variations of alleles that include an allele for brown eyes, blue eyes, and black eyes. In this case, a gene can have multiple alleles. An example of a multiple allele inheritance is a person’s blood type. There are three alleles for blood type – ABO, which would result in four possible genotypes that include A, B, AB, and O.

On the contrary, a polygenic trait occurs when a trait is controlled by two or more genes. For example, the wide range of skin color is caused by more than four different genes that control this trait. If a person who has a medium skin complexion has a genotype of AaBbCc, this means that there are 3 dominant genes and 3 recessive genes that are involved in this trait.

Genes have multiple alleles. These alleles can provide many phenotypes for a trait. For example, a gene for eye color has variations of alleles that include an allele for brown eyes, blue eyes, green eyes, etc. Having multiple alleles in a trait can make more random combinations of phenotypes during assortment. This is to ensure that there is always a genetic variation in all species.

An organism’s trait is formed due to an interplay of both genetics and environment. The way a gene works can be affected by environmental factors. For example, temperature, light, food, drugs, and toxins can cause changes in the DNA structure by affecting the functions of some encoded proteins, hormones, and enzymes. On example is the pigment gene in Himalayan rabbits. This gene is only active when the organism is placed in a temperature between 15 to 25 degrees Celsius. This indicates that the fur color of the Himalayan rabbit grows darker in cold temperature and it gets lighter in warm temperature.

The number of chromosomes in the organism’s gametes is 4.

In diploid organisms such as a rabbit, genes usually consist of two versions or *alleles*. In the given scenario, the gene for coat color has two types of alleles – *B* for black, and *b* for brown.

A homozygous black-coated rabbit would have a genotype of ***BB***. This is because a homozygous gene contains two of the same allele that corresponds to a specific coat color.

A heterozygous black-coated rabbit would have a genotype of ***Bb***. This is because a heterozygous gene contains two different types of alleles, and that one allele (*B*) is dominant.

Homozygous black = BB, heterozygous black = Bb

Meiosis is the process of cell division in germ line cells to form gametes. This process furthers sexual reproduction because each gamete has half the number of chromosomes of normal cells, so that when two gametes (one from each parent) combine, the correct number of chromosomes is preserved in the resulting zygote organism. This process is unlike mitosis, where the cells are simply replicated, preserving the number chromosomes.

In meiosis I, it starts with a diploid cell with a pair of homologous chromosomes. The crossing of genetic material between chromosome pairs occurs in this stage. Eventually, the diploid cell splits into two separate cells before meiosis II. This results in 2 haploid daughter cells with 23 chromosomes each.

In meiosis II, there is no chromosome replication that is involved because the chromosomes are no longer identical due to the assortment in meiosis I. These chromosomes are further separated which results to 4 haploid cells. Each haploid cell has 2 chromatids.

The chromosomes, not the individual genes, are the ones that are directly involved in the process of assortment during meiosis. It is because chromosomes consist of genes that are linked together. This means that the individual genes are all located on the same chromosome. When a chromosome moves, the genes on that chromosome also moves. This explains why linked genes are usually inherited because they are on the same chromosome.

If the allele for white wool (A) is dominant over the allele for black wool (a), the genotype of a white ram could be a homozygous AA or a heterozygous Aa.

To determine the probability of an offspring having a particular genotype, we can use a Punnett square diagram.

Here is a sample table showing the comparison of meiosis and mitosis:

The dominant allele for short hair is represented by capital A and the recessive allele for long hair is represented by letter a. If two heterozygous parents (Aa) are crossed, the possible genotypes of offspring are AA, Aa, Aa, and aa.

AA = short hair
Aa = short hair
Aa = short hair
aa = long hair

When two heterozygous parents (Aa) are crossed, the possible genotypes of their offspring are AA, Aa, Aa, and aa. This set of genotypes best fits the litter of eight puppies, which consists of six puppies with short hair and two puppies with long hair.

The dominant allele for rough coat is represented by capital R and the recessive allele for smooth coat is represented by letter r. When a heterozygous guinea pig (Rr) is crossed with a homozygous guinea pig (aa), the possible genotype of the offspring includes Rr and rr. Each genotype has a 50% chance of occurring in a particular generation. However, the occurrence of nine offspring with smooth coats in the heterozygous (Rr) and homozygous (rr) parents indicates that the recombination frequency of chromosomes in this crossover is low. If two genes on the same chromosome are close together, the recombination is low; hence, the crossover would rarely happen.

If two genes on the same chromosome are close together, the recombination is low; hence, the crossover would rarely happen. On the other hand, recombination frequency is high if the genes are distant from each other. In this case, the two genes that would usually assort independently are the ones that are far from each other. Therefore, the variation in the F2 generation would rarely happen since the genes in the chromosome are close to each other.

If two genes on the same chromosome are close together, the recombination is low; hence, the crossover would rarely happen. On the other hand, recombination frequency is high if the genes are distant from each other. Since genes M and S have a recombination rate of 5%, which is lower than the 8% recombination rate of genes S and P, this indicates that gene S is closer to gene M.

Ptarmigans change their feather color when seasons change in order for them to blend into their surroundings and to hide from their predators. In winter, their feathers would turn white so they can be camouflaged with the snow. During spring, they shed their feathers and grow new ones in either brown or gold color which lasts until the end of summer. Once the autumn comes, their feathers would fade to grayish brown.

This trait is formed due to an interplay of both genetics and environment. The way a gene is expressed can be affected by environmental factors such as temperature, light, food, drugs, or toxins.